[B.A.T.M.A.N.] required network to run

I am new to ad-hoc mobile networking, and have a few questions. I am just a little confused as to where batman fits in. Why do I need an active network to attach the batmand to? If I'm in a network can't I see all the other nodes already? What is batman buying for me if I have to create my own ad-hoc network? If I don't have to create my own ad-hoc network, how do I set up my linux boxes so that they have an active network that will discover the nodes and allow the batmand to run?

Thanks for your help Eric